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Did you know that there are tiny living organisms floating at the surface of most freshwater and saltwater bodies? Many of these organisms are dinoflagellates. In this lesson, we will investigate dinoflagellates to gain a better understanding of them.

Characteristics of Dinoflagellates

Have you ever seen photos of seawater lit up with a shiny, blue luminescence? Or maybe you’ve been warned against swimming in the ocean during a red tide? Both of these instances are caused by dinoflagellates, or unicellular eukaryotic organisms with two whip-like tails called flagella used for movement. They can be found in marine and freshwater environments all over the world.

Some of these organisms are photosynthetic, meaning they can synthesize their own food from carbon dioxide and water. Others are heterotrophic, meaning they cannot synthesize their own food. Some dinoflagellates have luminescent properties that make the sea appear to sparkle at night.Dinoflagellates are encrusted with plates made of a cellulose-like material and silica.

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Most dinoflagellates contain the pigments chlorophyll-a, chlorophyll-c and carotenoids, which allow them to undergo the process of photosynthesis to generate energy.Some species of dinoflagellates secrete toxins into the water. A population explosion of these organisms can cause the area they inhabit in the ocean to take on a red color and is commonly called a ‘red tide.’ During red tides, shell fish and other fish are deemed toxic to humans and should not be consumed.

Red tide

Dinoflagellates essentially have two means of reproduction. During normal conditions, they reproduce just like any cell, by asexual division. This means that new dinoflagellates break off from old dinoflagellates and grow into a separate organism.But under certain stressful conditions, like cold, starvation and lack of light, they undergo a different process to reproduce. Two dinoflagellates will join together in a process called fusion.

They will stay together through the stressful time in a semi-dormant state. Once conditions are again favorable, they break off into small pieces called cysts and grow into full-sized new organisms.

Examples of Dinoflagellates

There are approximately 4,500 species of dinoflagellates.

Common examples include:

  • Pfiesteria piscicida
  • Gonyaulax catenella
  • Noctiluca scintillans

Pfiesteria piscicida is a species of dinoflagellate often found off the coast of North Carolina. Scientists have concluded that it is responsible for killing large amounts of fish by secreting toxins. This species has an interesting feeding strategy.

It is known to use its toxins to kill fish, then wait to consume tissue that sloughs off from the decaying organisms. This makes it one of the few heterotrophic species of dinoflagellates.Gonyaulax catenella are dinoflagellates that spin greatly as they move by using their two flagella. They are also one of the well-known bioluminescent species of dinoflagellate, as they give off a blue-green glow in the waters they inhabit. Gonyaulax gives off toxins that can accumulate in the tissues of the shellfish that eat them to a level that can kill humans who eat the contaminated shellfish.Noctiluca scintillans is a species of heterotrophic dinoflagellate that feeds on plankton found in estuaries and shallow areas of the continental shelf. This species is commonly referred to as sea sparkle because it exhibits bioluminescence and becomes particularly bright when disturbed in the water.

It is also a toxic species noted for creating red tides in many parts of the world.

Noctiluca scintillans

Classification of Dinoflagellates

Because dinoflagellates can be viewed both as plant-like and animal-like, their classification has been debated amongst botanists, zoologists and paleontologists. The most widely accepted classification scheme is that all dinoflagellates are members of the kingdom Protista, division Dinophyta and class Dinophyceae. Dinoflagellates are then classified into many orders, genus and species based on characteristics such as feeding behavior, composition of their outer plate, overall anatomy and physiology.

Lesson Summary

Dinoflagellates are unicellular protists found floating in bodies of fresh or saltwater. They can be either photosynthetic autotrophs or heterotrophs, and they normally reproduce asexually unless conditions are unfavorable. There are a remarkable variety of dinoflagellates in the world, and they are able to have big impacts on their environment by releasing toxins or through bioluminescence.

Dinoflagellates Terms

Terms Definitions
Dinoflagellates unicellular eukaryotic organisms with flagella used for movement, can be found in marine and freshwater environments
Photosynthetic synthesize food from carbon dioxide and water
Heterotrophic organisms that do not synthesize their own food
Pfiesteria piscicida species of dinoflagellate often found off the coast of North Carolina
Gonyaulax catenella dinoflagellates that spin as they move by using their two flagella
Noctiluca scintillans species of heterotrophic dinoflagellate that feeds on plankton found in estuaries, shallow areas of the continental shelf

Learning Outcomes

When this video concludes, you will be prepared to:

  • Define dinoflagellate
  • Explain where dinoflagellates may be found
  • Describe examples of common species of dinoflagellates
  • Recall how dinoflagellates are classified

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